keyfilter

Does not allow to enter 0 at all. The regex seems to be applied on each character, rather than on the input as a whole.

HTML

<script src="https://raw.github.com/akzhan/jquery-keyfilter/master/jquery.keyfilter.js"></script>
<input id='test' type="text"/>

JavaScript

$('#test').keyfilter(function(c) {
    return c != 'a';
});